This invention relates generally to inflators for use in inflating inflatable restraint airbag cushions, such as used to provide impact protection to occupants of motor vehicles. More particularly, the invention relates to inflators having multiple or plural stages or levels of inflation gas output and as such may be used to provide an inflation gas output which is adaptive to factors such as one or more crash and occupant conditions.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an "airbag," that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins being inflated in a matter of no more than a few milliseconds with gas produced or supplied by a device commonly referred to as an "inflator."
Various types of inflator devices have been disclosed in the art for the inflation of an airbag such as used in inflatable restraint systems. One type of known inflator device derives inflation gas from a combustible pyrotechnic gas generating material which, upon ignition, generates a quantity of gas sufficient to inflate the airbag.
Such inflator devices commonly include or incorporate various component parts including: a pressure vessel wherein the pyrotechnic gas generating material is burned; various filter or inflation medium treatment devices to properly condition the inflation medium prior to passage into the associated airbag cushion and a diffuser to assist in the proper directing of the inflation medium into the associated airbag cushion.
In view of possibly varying operating conditions and, in turn, possibly varying desired performance characteristics, there is a need and a desire to provide what has been termed an "adaptive" inflator device and a corresponding inflatable restraint system. With an adaptive inflator device, output parameters such as one or more of the quantity, supply, and rate of supply of inflation gas, for example, can be selectively and appropriately varied dependent on selected operating conditions such as ambient temperature, occupant presence, seat belt usage and rate of deceleration of the motor vehicle, for example.
While such adaptive systems are desirable, they typically require the inclusion of additional components as a part of the associated inflator device and such as may undesirably increase one or more of the size, cost and weight of the inflator device. For example, various proposed or currently available dual stage inflator devices appear based on the principal of packaging together two separate inflators. As a result, such inflator combinations commonly include two distinct pressure vessels, two sets of filter or inflation gas treatment components, one for the output of each of the pressure vessels, and two distinct diffusers, again one for the output of each of the pressure vessels. Thus, it has been difficult to provide an adaptive inflator which will satisfactorily meet the size, cost and weight limitations associated with modern vehicle design, particularly as it pertains to driver side applications.
More specifically, driver side airbag inflator devices commonly have the general form of a flattened, disk-shaped circular cylinder typically or generally having a length (sometimes referred to as "height") to diameter ratio of about 0.5 or less. For example, a typical driver side inflator might be about 40 mm in length or height and about 80 mm in diameter. An inflator device having such shape and size provides a familiar and convenient package for insertion in a corresponding or associated airbag module housing.
Thus, there is a need for an adaptive inflator device of simple design and construction and which will meet the size requirements for vehicles, especially for driver side applications. In particular, the growing use or desire to use adaptive output inflators has made it generally desirable for the shape of adaptive output inflators to not significantly depart from the typical design envelope associated with prior single stage inflators and to thereby preferably facilitate the incorporation of such adaptive output inflator devices into various vehicle designs and to minimize or avoid significant design changes to the mating hardware included with particular airbag modules.
At least partially in response to such need, a new type of adaptive inflator device, the subject of the above-identified patent application, U.S. patent application Ser. No. 09/027,114, has been developed. In accordance with one embodiment disclosed therein, such an airbag inflator device includes a housing defining a first chamber which in an at rest or static state or condition contains a quantity of a first gas generant material ignitable to produce first combustion products including a first inflation gas. The first chamber has a plurality of spaced apart gas exit ports adapted to open to permit passage of the first inflation gas from the airbag inflator. The first chamber also contains a second chamber which in an at rest or static state or condition contains a quantity of a second gas generant material ignitable to produce second combustion products. The second chamber includes an exit orifice adapted to open to place the second combustion products in fluid communication with the contents of the first chamber. The airbag inflator also includes a first igniter device operatively associated with the first chamber and a second igniter device operatively associated with the second chamber.
While such an inflator device can be generally effective in overcoming at least some of the shortcomings of prior art inflator devices, a further improved adaptive inflator device may be desired for use in at least certain specific applications. For example, if a traditional cylindrical driver side airbag inflator shape is used for an adaptive output inflator, such as includes two or more separate pyrotechnic charges, special design restrictions may need to be imposed on the internal arrangement of the inflator in order to properly maintain desired separation of such distinct pyrotechnic charges. As will be appreciated, such charge separation restrictions are generally not needed or included in typical single stage inflator devices.
Typically, the most significant inflator design and operational requirement resulting from a desire to properly maintain separation of distinct pyrotechnic charges is evidenced through design features included to maintain either and, preferably, both, a pressure and a thermal boundary between the respective pyrotechnic charges until such time that the particular charge is desired to be ignited. The most usual instance of such desired separation is in the case of a two-stage inflator having a first chamber which contains or includes a first pyrotechnic charge and a second chamber which contains or includes a second pyrotechnic charge. In practice, the maintenance of such charge separation necessitates that the second pyrotechnic charge be isolated from the combustion products resulting from the combustion of the first pyrotechnic charge. For example, the second pyrotechnic charge is desirably isolated from the product gases resulting from the combustion of the first pyrotechnic charge such that such combustion product gases cannot enter into the chamber housing the second pyrotechnic charge and result in the ignition thereof.
Conversely, when it is desired that the second stage pyrotechnic charge be ignited, the inflator design and operation desirably will permit the inflation gas resulting from the combustion of the second pyrotechnic charge to flow into the first chamber and ultimately exit from the inflator, such to facilitate inflator design and the efficient operation thereof.
In an effort to address the need for such charge isolation, at least certain designs make use of what is known as a burst disk. Typically, burst disks are made of relatively thin metal and are designed and selected to rupture or otherwise open when a sufficient predesigned pressure is applied thereagainst. While such applications of burst disks are generally effective in maintaining desired pressure boundaries between respective pyrotechnic charges of at least certain multiple charge-containing inflator devices, such burst disk uses are generally not fully effective in maintaining required or desired temperature boundaries between respective pyrotechnic charges. In particular, such burst disks are typically relatively thin and do not provide sufficient desired thermal isolation between adjacent charges. Further, such uses or applications of burst disk components generally necessitate the inclusion of certain additional supporting components such as one or more support plates. As will be appreciated, the inclusion of such additional component or the like can undesirably complicate manufacture, production, and operation of the resulting device as well as undesirably increase either or both the weight or cost associated with such devices. Alternatively or in addition, burst disks are commonly welded in place. Such weld processing can undesirably add to the time and expense of production and may additionally raise the potential for leakage therethrough, such as may hinder or defeat desired operation.
Thus, there is a need and a demand for an adaptive inflator device and operation which will facilitate such charge isolation until the desired actuation thereof and thereupon cooperate or function to permit the desired flow of the combustion products resulting from the combustion of the second pyrotechnic charge into the first chamber and ultimately to exit from the inflator. Further, there is a need and a demand for such an adaptive inflator device of relatively simple design and construction and, in turn, comparatively, low or reduced cost. In particular, there is a need and a demand for such an adaptive inflator device which will meet the size requirements for vehicles, especially for driver side applications.